Manufacture of carboxymethyl cellulose



Patented May 19, 1953 MANUFACTURE OF CARBOXYMETHYL CELLULO SE Arthur Hodge, James Gordon Napier Drewitt,

and John Downing, Spondon, near Derby, England, assignors to British Celanese Limited, a corporation of Great Britain No Drawing. Application September 20, 1950, Serial No. 185,906. In Great Britain October 21 Claims.

This invention relatesto the manufacture of carboxymethyl cellulose. 7

In accordance with the commonpractice the term carboxymethyl cellulose is employed in the present specification to include the sodium salt, in which form the compound is normally obtained and used. References to solubility, viscosity and other properties are to-be taken as relating to the sodium salt.- If the free acid is required it can easily be obtained by treating the sodium salt with an acid, e. g. hydrochloric acid.

It is known that carboxymethyl cellulose can be made by mixing chloracetic acid or sodium chloracetate with alkali cellulose and milling the mixture, e. g; in a Werner-Pfleiderer mixer. The constitution and properties of carboxymethyl celluloses so obtained, e. g. their degree of substitution, solubility, viscosity and homogeneity, may vary widely, and their commercial utility and value are likewise variable. Moreover the amounts of alkali and chloracetic acidor sodium chloracetate employed exceed by a considerable proportion the amounts theoretically required, so increasing the cost of the carboxymethyl cellulose. I

It is an object of the present invention to provide novel conditions for the manufacture of carboxymethyl cellulose which shall reliably give a water-soluble product having a satisfactory degree of homogeneity and which at the same time shallbev economical with respect to the amount of alkali j and carboxymethylating agent employed.

According to the invention, cellulose is impregnated with caustic soda by immersing it in a caustic soda solution of concentration 15-33%,

- obtained, and the mixture is milled at a temper- :ature kept below 25 C; Advantageously, the temperature of the caustic sodasolution in which the cellulose is. immersed. is above .65" .C. and especially between 75 and85 C.

In a preferred method, the cellulose is immersed in a caustic soda solution of concentration 21-26%, and the impregnated cellulose is subjected to a low pressure-only (i. e.a-pressure below about 7 5 p. s. i. g.) and especially to a pressure of about 40-50 p. s. i. g.,'until the molecular ratio ,of-the'caustic soda to the cellulose has been reduced to between-2.0 and 2.5-and especially be- 2 a tween 2.0 and 2.3. Chloracetic acid is mixed with the alkali cellulose so obtained, and the mixture is milled at a temperature which initially and for at least the greater part of the milling time is between 10 and. 20 C.

By employing the conditions set out above, it

' is possible to make use of as little as 0.75 or 0.65

molecular proportions of chloracetic acid for each molecular proportion of cellulose (reckoned as CsI-ImOs) and still obtain a homogeneous water- 'soluble product, though larger amounts, e. g. up

desirable than the use of the free acid.

A further condition which we have found it most advantageous to observe is that the amount of caustic soda in the alkali cellulose should not exceed 1.5 times the equivalent of the amount of chloracetic acid to be employed (taking into account both'the carboxyl group and the chlorine atom) in other words themolecular ratio of the caustic soda to the chloracetic acid should not exceed 3:1. It will be noted that it is only possible to make use of a corresponding ratio (i. e. less than 1.5-times the equivalent) with sodium chloracetate, without going outside the conditions characterising the invention and set out above, by the use of an excessive quantity of the carboxymethylating agent; it has already been pointed out that in actual practice it has been found preferable to use free chloracetic acid.

It will be noted that the molecular ratio of alkali to cellulose is expressed in terms of the analytical ratio and not primarily in terms of the wet/ dry ratio usually employed. We have found-that the wet/ dry ratio does not give a general measurement of the ratio of alkali to cellulose which is certain enough for the present purpose, partly because some alkali is taken up by the cellulose from'the solution and partly'because some part of the cellulose usually dissolves in the alkali solution. Both these eifects operate in the same direction, namely to increase the true ratio of alkali to cellulose over the value calculated from the wet/dry ratio. For a givencellulose and given conditions of impregnation and pressing (including concentration and temperature of the alkali solution) the relationship between the true ratio. and the wet/dry ratio is The alkali cellulose is preferably made by im;

mersing cellulose, e. g. wood pulp in sheet form,

in the caustic soda solution undenthespecified: conditions for a considerable time, e. g. between. about 30 minutes and 1 or 1 hours or more, and

then squeezing the cellulq means of a ram operating aga ailarge nurnbeii of impregnated sheets. Advantageously the cel-- lulose may be impregnated and pressed in one and the same vessel in thekilown manner.- I;

desired, however, the alkalfcllulose may be made by feeding the cellulose in sheet form continuously first through a bath of the, caustic soda solution, and then through one or more pairs oi-soue rollers.

sad; b fo e. bein charge wea e satis s e -ts :y its i l l 'im t This ma he 41 for'exam'ple ina Bridge Banbury mixing machine tt st. we

a r d- Siastg f T t a -51 st's-5,

es nd,bathe.. urpqsesiqm hitis tdhehsd hus bep 'esen eptsa ts n aacarboxymethyi 1 e i 9 disa talltflsai tmay be su ficient to heiitralis han rema n ng-caustic soda, by i har s means of carbon dioxide or hydrogen chloride, and then to dry the carboxymethyl cellulose, for instance by heating it in a current of air. If a substantially pure product is required the caustic soda, instead of being neutralisecl; mam-be washed out of the crude carboxymethyl cellulose by means of an aqueous alcohol, for example aqueous methanol or ethanol of concentration about 75:;%-,8;'57Q*, a t-room temperature or at a higher temperature up to the boiling point of the alcohol. The invention is illustrated by the following eauties:

Example I A purified wood pulp in sheet form was immersed for-, lmouriin 23% aqueous caustic soda atBJlbC. andvzas, then pressed at 40-50 p. s. i. g. until the molecularratio of caustic soda to cellulose. (as determined by analysis) was 2.10 (Wet/ dry ratio 2.77)

The all a1i cellulose so pro duced was broken up in ahammer' mill and'charged- -to ajacketed Werner -Pfieiderer mixer: lined-withstai-nless steel and :haying stainless steel blades, andwas; milled therein for about 2- hours at a temperature'kept fi'l 'ween 15 and C: by passing chilled brine through the jacket; Chloracetic "aicid wast-hen addedfin' three" stages at; intervals o f- 959 minutes, O. ;H1 olecula;r proportion for each. molecular proportion of --cellulosein-the;mixture- (as deter-- mined by; theanalysis of the alkali cellulose) beingadded at each stage; milling was continued throughout and for a-fur ther 'l hoursa fter' the finial additiomand jthe' temperature W askept between lband 2t -c until the end ofithe period, when it; was allowed to rise to-2-2= The product was discharged from the -Werner Pfleiderer mixer into a vat whereeitwas; allowed to staridler; lzflhours at-;about 20?- C; Partwvas then thoror l ly washed With-3G aqueous methanol andp t was treated with carbon diox-Ldato neutralise residual caustic soda but was not otherwi q purif ed; Both fractions-dissolved substantially completely ingvater; r 2 aqueous solutions having cla'rities75 and (water MO 573-) and viscosities at 20 C. and '74 cps. respectiyely, degree 3 of substitution was 0-.62- ('i. v e. 0.63 earboxymethyl groupswere p-resent for each anh-ydrocose unit of thecelluleselg the-prod ucts w ere' fi rous instructure. Thewashed product contained about 96% of -sodium-carbbxymethyl cellulose and 4%--of sodium-chloride,- be ing substantiallyfree fromsodium'carbonateand ee ium lwellate.

r-differential purifiedavood-pul-pwas immersed for -1 hour i-n a 22% caustic --s0da solution-M180 C. andjthen pressed-"atAo M 50 pr s-.--i-. gun-til the molecular 1 ratio ot-'gcau stic 'sodaioscellulos -was 2.22 the-alkali cellulose sotobtained-was milled,

firstalone and then,;after-adding chloraceticacid,

i-P i t Qdnulawese w the tneatment d in ie-5. L, x ept hat? the subsequent milling the temperature was kept between and C. The washed product had a viscosity of about 4 cps. in 2% aqueous solution at 20 C.

It will be seen that by observing the conditions laid down in the present specification, it is possible to obtain a water-soluble carboxymethyl cellulose having very satisfactory properties, even though the amounts of the reactants employed are much lower than usual.

Having described our invention, what we desire to secure by Letters Patent is:

1. Process for the manufacture of carboxymethyl cellulose which comprises impregnating cellulose with caustic soda by immersing the cellulose in a caustic soda solution of concentration 15%-'33% at a temperature above 50 C., subjecting the impregnated cellulose to pressure until the molecular ratio of caustic soda to cellulose, as determined by analysis, reckoning the cellulose as Cal-1100s, is between 2.0 and 3.1 mixing a compound selected from the group consist ing of chloracetic acid and sodium chloracetate with the alkali cellulose so obtained, and milling the mixture at a temperature-kept below C.

2. Process for the manufacture of carboxymethyl cellulose which comprises impregnating cellulose with caustic soda by immersing the cellulose in a caustic soda solution of concentration 21%-26% at a temperature above 50 C., subjecting the impregnated cellulose to pressure until the molecular ratio of caustic soda to cellulose, as determined by analysis, reckoning the cellulose as Cal-11005 is between 2.0 and 3.1, mixing a compound selected from the group consisting of chloracetic acid and sodium chloracetate with the alkali cellulose so obtained, and milling the mixture at a temperature kept below 25 C.

3. Process for the manufacture of carboxymethyl cellulose which comprises impregnating cellulose with caustic soda byimmersing the cellulose in a caustic soda solution of concentration 21%-26% at a temperature of '75-85 C., subjecting the impregnated cellulose to pressure until the molecular ratio of caustic soda to cellulose, as determined by analysis, reckoning the cellulose as C6Hl005, is between 2.0 and 3.1, mixing a compound selected from the group consisting of chloracetic acid and sodium chloracetate with the alkali cellulose so obtained, and milling the mixture at a temperature kept below 25 C.

4. Process for the manufacture of carboxymethyl cellulose which comprises impregnating cellulose with caustic soda by immersing the cellulose in a caustic soda solution of concentration 21%26% at a temperature of 7585 C., subjecting the impregnated cellulose to pressure until the molecular ratio of caustic soda to cellulose, as determined by analysis, reckoning the cellulose as CeHioOs is between 2.0 and 2.5, mixin a compound selected from the group consisting of chloracetic acid and sodium chloracetate with the alkali cellulose so obtained, and milling the mixture at a temperature kept below 25 C.

5. Process according to claim 4 wherein 0.75- 1.25 molecular proportions of the compound selected from the group consisting of chloracetic acid and sodium chloracetate are employed for each molecular proportion of cellulose, reckoned as CeI-IroOs.

6. Process according to claim 4 wherein 0.75- 125 molecular proportions of the compound selected from the group consisting of chloracetic acid and sodium chloracetate are employed for each molecular proportion of cellulose, reckoned 'as Cal-11005, wherein the milling is carried on for at least eight hours, and at the beginning and during the greater part of this time the temperature of the mixture is between 10 and 20 C.

7. Process for the manufacture of carboxymethyl cellulose which comprises impregnating cellulose with caustic soda by immersing the cellulose in a caustic soda solution of concentration 18%-30% at a temperature above 65 0., subjecting the impregnated cellulose to a light pressure until the molecular ratio of caustic soda to cellulose, as determined by analysis, reckoning the cellulose as CeHmOs, is between 2.0 and 3.1 mixing chloracetic acid with the alkali cellulose so obtained, and milling the mixture at a temperature kept below 25 C.,

8. Process for the manufacture of carboxymethyl cellulose whichcomprises impregnating cellulose with caustic soda by immersing the cellulose in a caustic soda solution of concentration 2l%-26% at a temperature above 65 C., subjecting the impregnated cellulose to a light pressure until the molecular ratio of caustic soda to cellulose, as determined by analysis, reckoning the cellulose as Cal-11005 is between 2.0 and 3.1, mixing chloracetic acid with the alkali cellulose so obtained, and milling the mixture at a temperature kept below 25 C.

9. Process for the manufacture of carboxymethyl cellulose which comprises impregnating cellulose with caustic soda by immersing the cellulose in a caustic soda solution of concentration 21%-26% at a temperature of -85 C., subjecting the impregnated cellulose to a light pressure until the molecular ratio of caustic soda to cellulose, as determined by analysis, reckoning the cellulose as C6H10O5, is between 2.0 and 3.1, mixing chloracetic acid with the alkali cellulose so obtained, and milling the mixture at a temperature kept below 25 C.

10. Process for the manufacture of carboxymethyl cellulose which comprises impregnating cellulose with caustic soda by immersing the cellulose in a caustic soda solution of concentration 2l%-26% at a temperature of 75-85 C., subjecting the impregnated cellulose to a light pressure until the molecular ratio of caustic soda to cellulose, as determined by analysis, reckoning the cellulose as CsHmOe, is between 2.0 and 2.5, mixing chloracetic acid with the alkali cellulose so obtained, and milling the mixture at a temperature kept below 25 C.

11. Process according to claim 10 wherein 0.75-1.25 molecular proportions of the compound selected from the group consisting of chloracetic acid and sodium chloracetate are employed for each molecular proportion of cellulose, reckoned as Cal-11005.

12. Process according to claim 10 wherein 0.75-1.25 molecular proportions of the compound selected from the group consisting of chloracetic acid and sodium chloracetate are employed for each molecular proportion of cellulose, reckoned as CsHmOs, wherein the milling is carried on for at least eight hours, and at the beginning and during the greater part of this time the temperature of the mixture is between 10 and 20 C.

13. Process for the manufacture of carboxymethyl cellulose which comprises impregnating cellulose with caustic soda by immersing the cellulose in a caustic soda solution of a concentration 18%-30% at a temperature above 65 C., subjecting the impregnated cellulose to a light pressure until the molecular ratio of caustic soda to cellulose, as determined by analysis, reckoning the 

1. PROCESS FOR THE MANUFACTURE OF CARBOXYMETHYL CELLULOSE WHICH COMPRISES IMPREGNATING CELLULOSE WITH CAUSTIC SODA BY IMMERSING THE CELLULOSE IN A CAUSTIC SODA SOLUTION OF CONCENTRATION 15%-33% AT A TEMPERATURE ABOVE 50* C., SUBJECTING THE IMPREGNATED CELLULOSE TO PRESSURE UNTIL THE MOLECULAR RATIO OF CAUSTIC SODA TO CELLULOSE, AS DETERMINED BY ANALYSIS, RECKONING THE CELLULOSE AS C6H10O5, IS BETWEEN 2.0 AND 3.1 MIXING A COMPOUND SELECTED FROM THE GROUP CONSISTING OF CHLORACETIC ACID AND SODIUM CHLORACETATE WITH THE ALKALI CELLULOSE SO OBTAINED, AND MILLING THE MIXTURE AT A TEMPERATURE KEPT BELOW 25* C. 